Many areas of biotechnology involve regulating the expression of one or more genes of interest by applying an external agent. Typical approaches for regulating gene expression involve natural or engineered transcription factors that activate or inhibit expression of a specific gene in response to a chemical agent [Gossen and Bujard, Proc. Natl. Acad. Sci. USA, 89:5547, 1992; Rivera, et al., Nat. Med., 2:1028, 1996; Yao and Evans, Proc. Natl. Acad. Sci. USA, 93:3346, 1996; Wang, et al., Proc. Natl. Acad. Sci. USA, 91:8180, 1994]. Transcription factors often are introduced into a cell using DNA constructs that express a transcription factor and a gene of interest.
Stable activation or inhibition of a transcription factor typically requires a continuous application of a chemical agent. For example, continuous activation of a LacI-repressible promoter typically requires the continuous presence of the chemical agent isopropyl β-D-thiogalactopyranoside (IPTG). However, continuous application of a chemical agent is often undesirable because it can have confounding or deleterious effects on the cell or tissue to which it is applied. In addition, the amount of chemical required for continuous application can be very costly, especially when a large volume of cell culture is involved. Therefore, there is a need in the art for methods and compositions for regulating the expression of a gene of interest without the continuous application of one or more stimulating agents.